C2

Comparing materials and measuring properties

• - Each material has properties that make it suitable for the job it's doing
• rubber is used for car tyres because it is hard and elastic
• fibres are used to weave cloth into clothes
• plastics keep their shape when moulded into objects like washing-up bowl
• - different plastics have different properties, manufacturers make products by choosing plastics that give the best properties
• -properties describe how a material behaves
• Melting point is the temperature at which a solid turns into a liquid
• Tensile strength is the force needed to break the material being stretched
• Compressive strength is the force needed to crush a material when it's being squeezed
• Stiffness is the force needed to bend a material
• Hardness is how well a material stands up to wear. Hardness can be compared by scratching two materials together
• Density is the mass of a given volume of a material. It compares weight and size.
• - some properties depend on the size and shape being tested
• - density = the mass of a given volume of the material. It compares how heavy something is for its size.
• - the effectiveness and durability of a product depends on the material used to make it
• - rubber is an elastic material that bounces back when a force is removed, different types of rubber have different compressive stengths and hardness

Errors and Variation in Measurement

• - A single result may vary, so repeats are needed
• - a result which is very different might be an outlier - an incorrect resukt
• - calculating the mean is a good way to estimate the true value
• - the range is the smallest to the largest result, excluding outliers
• -we can never be sure if a set of measurements gives the true value
• - errors in measurement produce variation in data
• - outliers can be discarded if an error occured

Natural and Synthetic Materials

• - All the materials we use re chemicals, or mixtures of chemicals
• Metals are shiny, malleable and electrical conductors
• Ceramics include clay, glass and cement. They are hard and strong
• Polymers are large molecules used for rubber, plastics and fibres
• Concrete is a mix of sand and cement
• Bronze is a mix of tin and copper
• - Natural materials from living things which need little processing eg. cotton and paper and silk
• -Other natural materials that are raw are crude oil and iron ore
• - Synthetic materials are manufactured by chemical reactions using raw materials
• -They have replaced natural materials because:
• some natural materials are in short supply
• they can be designed to give certain properties
• they are often cheaper and can be made in the quantities needed

Crude oil and using hydrocarbons

• - Crude oil is a mix of thousands of hydrocarbons. Hydrocarbons are compounds of carbon and hydrogen atoms
• most hydrocarbons from crude oil is used as fuels
• when fuels burn in O2, CO2 and H2O are made
• - Burning a fuel like methane is a chemical reaction, so atoms are rearranged into new products
• - The number of atoms of each element in the reactants must be the same as the products
• - Crude oil consists mainly of hydrocarbons, which are chain molecules of varying length up to 100 carbon atoms long
• - As crude oil is a mixture, its composition varies from place to place
• - Around 3% of crude oil, mainly smaller hydrocarbon molecules is used to synthesis other chemicls. Examples of synthesized chemicals from oil are ethanol and plastics

Separating out the substances in crude oil

• - Crude oil is separated by fractional distilliation:
• The oil is heated up which turns it all into gases
• The distillation tower gets cooler as it gets higher
• Gas molecules condense into liquids when they call
• Liquids with similiar boiling points collect together. We call these fractions.
• - Hydrocarbons in each fraction have boling points within a range of temperatures
• -Moleule chai lengths are similiar sizes which each fraction
• -The smallers the molecule chain length the lower the boiling point as less force is
• needed to break it because there is less force between the molecules
• - Attractive forces exsist between molecules in crud eoil, holding them together
• - As the hydrocarbon length increases, forces between the molecules also increases
• - Larger molecules need more energy to break them out of liquid to form a gas, so have higher boiling points

Making Polymers

• - A polymer is a large molecule made by joining many smaller molecules called monomers
• - A polymer can have a chain of anything from hundreds to millions of carbon atoms
• - A polymer is made by a process called polymerization
• - Polymers with better properties mean some old materials can be replaced
• - Ethene is a monomer used to make ploythene
• - Different monomers make different polymers
• - PET is a polymer used to make drinks bottles. It is clear, strong, has a low density and doesn't shatter. This makes is a superior material to glass.
• - Polymer chains can be altered by replacing hydrogen atoms with atoms or groups of atoms
• - Materials choice will depend on comparing properties for different jobs, cost will be a factor

Attractive molecules and Polymer Differences

• - Small forces attract molecules to each other
• - The forces are strongest when the molecules are close
• -The stronger the force:
• the more energy is needed to separate the molecules
• the higher the melting point
• - Polymers can be made with properties that make them suitable for a range of different uses
• -The properties of polymers depend upon how their molecules are arranged and held together
• - Low density polyethene has long molecules with branches. The branches keep molecule chains apart, so the forces are weak. Items eg. plastic bags are weak and flexible, soft and have low melting points
• - High density polythene has long chains but no branches, so the molecules are aligned close together, it makes things stronger, stiffer and used for long lasting things such as water pipes
• -HDPE has a high degree of crystalline, this means there are lots of areas with regular patterns in the way hat the molecules line up
• - High Crystalline polymers are strong, with high melting points but can be brittle

Improving Polymers

• - Making a molecule chain longer makes it stronger
• -Longer chains need for force to separate them and therefore have higher melting points
• -Plastisicers are used to make a polymer softer.They are small molecules inserted into polymer chains to keep them apart, weakening the forces between them
• -Plasticised PVC is still hard wearing and waterproof, but it is also flexible, making it a suitable material for raincoats
• - Thermoplastics soften when heated and can be molded into shape
• -Thermosetting Plastics do not soften when heated =. They contain cross-links which lock the molecules together so they cannot melt.
• -Crysallinity can be increased by removing branches on the main polymer chain and making them lye as flat as possible. This is so they can line up neatly
• -Drawing polymers through tiny holes when heated makes the chains line up, this makes a higher tensile strength fiber
• -Materials which have been treated in this way include bullet proof vests and sail material.

Nanotechnology

• Nanoparticles are materials containing thousands of atoms
• -they occur naturally, salt in seaspray
• -occur by accident eg particulates
• -can be designed in labs
• It is the use and control of very small structures, measured in nanometres, one millionth of a mm
• An atoms is 1/10 of a nm in diameter
• They can be built up from individual atoms, they structures are about the same size as some structures
• Carbon nanotubes are being designed in labs
• Some are effective catalysts as they have large surface areas, increasing the surface area gives more space for reactions to take place
• It can increase when a lump of solid is cut into bits
• Nanotechnology builds structures from 10 atoms across - 1000 atoms across
• While the diameter of nanoubes is measure in nm they can be mm long
• - nano particles have large surface areas so they show different properties to larger particles of the same material

Using nanoparticles

• Silver nanoparticles are good at killing bacteria. They can be: added to fibres and woven into socks; put into wound dressings and put into food containers
• Titanium oxide nanoparticles are put in sun cream, they make it transparent and absorb UV
• They can be mixed with other materials eg.metal to make composites
• Composite materials are stronger and harder wearing, adding nanoparticles to:
• - plastic sports equipment makes it stronger
• -tennis balls makes them bouncier for longer
• -rubber in tires makes them harder wearing
• Nanotechnology- the science of making and using nanoparticles
• Graphite forms in strong sheets that serparate easily. Individual graphite sheets one-atoms thick are known as graphene sheets
• they can be rolled into carbon nanotubes, this is a super-strength material

Are nanoparticles safe?

• Silver nanoparticles can wash out of the clothes they were in and get in the sewage works
• Sewage works use bacteria to clean water, silver nanoparticles could kill these useful bacteria
• They could kill many microorganisms in the environment
• They are also used in cosmetics, they are added to things already used and tested, they are small enough to pass through skin into blood, the possible medical effects are not yet known
• One fear is that they might be breathed in and cause lung and brain damage
• Some people think because they occur naturally they aren't a threat, some disagree because new nanoparticles with new properties have been manufactured
• No one knows if solid nanoparticles can escape into air
• Risk is defines as the chance the event occurring, consequence is if it is